Wood signs are continuously exposed to rain, sunlight, and temperature extremes. Over time, exposure to water and ultra-violet radiation structurally and chemically changes the surface of wood and leads to the set of characteristics known as weathering. These characteristics include loss of color, loss of natural aromatic oils and waxes, checking and fracturing of the wood surface, and growth of molds, fungus, and bacteria that cause further chemical and structural degradation.
Wood signs are normally coated with varnish, shellac, polyurethane, linseed oil, or other common finishes. These finishes are dissolved in a volatile hydrocarbon solvent and applied as a liquid to the surface of the sign. Following application, the volatile hydrocarbon solvent evaporates and the long polymer molecules of the finish chemically interact by forming covalent cross-links with one another to form a hard, water-resistant finish. The finish prevents the loss of natural oils and waxes from the wood, and prevents water and living organisms from entering the wood. In addition, these finishes are clear, so that the natural color and patterns of the wood surface remain visible through the finish. Unfortunately, all of these finishes break down, over time, when exposed to water and sunlight. UV-radiation causes chemical damage to the polymer molecules, breaking polymer backbones and crosslinks and leading to loss of integrity of the finish. These common finishes generally deteriorate and become permeable to water within several years. The only remedy is to remove the degraded finish, along with some amount of the wood surface, and refinish the sign. This is an expensive and time consuming procedure, and one that can be done only a limited number of times.
A need has therefore been recognized for a durable, weather-resistant finish for wood signs that preserves the natural color and pattern of the wood surface.